The strongest earthquake to hit New Zealand's capital of Wellington in 150 years is raising seismic alarms, “but none of the locals are diving under desks or sheltering in doorways,” the New Zealand Herald says. That's because the quake's energy, enough to qualify as a magnitude 7 event, is being released slowly. It's a phenomenon we've seen not too long ago in California. From the Smart News blog at Smithsonian.com:
In a normal earthquake, the Earth lurches, releasing in some cases multiple atomic bombs-worth of energy in seconds. The shaking and rolling felt at the surface makes buildings tumble and gas lines rupture—an unpredictable disaster that seems to strike out of nowhere.
But the Wellington earthquake is different. What’s happening near Wellington is that that same amount of energy, and the same amount of movement of the Earth’s surface, is being spread out over months and months. It’s still a magnitude 7 earthquake, it’s just a gradual one.
Wellington’s residents aren’t in a panic, says GeoNet, because the Wellington quake is a strange type of earthquake known as a “slow slip earthquake,” a style of tremblor that scientists only really discovered over the past decade.
Unlike earthquakes, which seem to occur almost at random, slow slip earthquakes can be recurrent. They come and go, sometimes happening annually. In New Zealand, the Wellington quake is actually the third of a set: similar earthquakes were detected in 2003 and 2008, says GeoNet.
The scientists have actually been studying the slow-slip type of earthquake for longer. Back in 1996, Nature ran a paper on bore tests that revealed a slow-release quake along the San Andreas Fault. Here's more reading on slow earthquakes.
Photo: Cleaning up damage from a 2011 New Zealand earthquake. Geof Wilson on Flickr